A significant proportion of the mobile users worldwide are prepaid users, having a pre-paid subscription with an operator. For most of the prepaid users online charging is used. With intelligent network (IN) solutions it is common that the Online Charging System (OCS) used has the capability to initiate call announcements towards the prepaid user. These announcements can be generated before call setup (pre-call announcements), during a call or at the end of the call. Pre-call announcements are used for a variety of reasons (e.g. welcome message, account balance information, barring reason). Announcement during a call is often a short warning that the account balance is very low (call cut off warning, often in a form of a tone) and announcement at the end of the call is used when the call has been cut off due to empty account.
For mobile prepaid users in an IP Multimedia Subsystem (IMS) network using a Multimedia Telephony Service (MMTel) application server (AS), the AS can produce some announcements based on information received in attribute value pairs (AVP) from the OCS over an Ro interface (the Ro interface will be described in further detail below). Such announcements can primarily be based on Low-Balance-Indication AVP, Final-Unit-Indication AVP and the received result-code.
Reference should be made to RFC 4006 (Diameter Credit Control), RFC 3588 (Diameter Base Protocol), 3GPP TS 24.229 (Internet Protocol (IP) multimedia call control protocol based on Session Initiation Protocol (SIP) and Session Description Protocol (SDP); Stage 3), 3GPP TS 32.260 (IMS Charging), 3GPP TS 32.240 (Charging architecture and principles), 3GPP TS 32.299 (Telecommunication management; Charging management; Diameter charging applications).
The present applicant has appreciated that there is a need for improved announcement services for mobile prepaid users of a Multimedia Telephony Service (MMTel) in an IP Multimedia Subsystem (IMS) network.